Re: Are circular relationships a bad thing in ER-modeling?

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"Laconic2" <laconic2_at_comcast.net> wrote in message news:AMSdnWarttWVwQvd4p2dnA_at_comcast.com...
>
> "x" <x-false_at_yahoo.com> wrote
> > Show is an ENTITY or a RELATIONSHIP ? :-)
>
> > What you usually use to relate two entities in ER-modeling ?
>
> Sometimes, things that start out as RELATIONSHIPS eventually become
> recognized as ENTITIES in and of themselves. An example:
>
> A "confirmation" in an airline reservation system. Initially this can be
> modeled as a ternary relationship between a flight, a date, and a
passenger.
> But, as data like "confirmation status", and "confirmation number" get
> added, it is sometimes useful to model a confirmation as an entity in
its
> own right. This is sometimes called "reifying".

Because only ENTITIES can have ATTRIBUTES in ER modeling ? This is the ONLY criterion ?

> .................
>
> You generally don't "use" anything to IMPLEMENT the relationships in
> ER-modeling. You can represent relationships in an ER diagram by the
lines
> that connect the boxes. But how you implement them depends on your
> implementation environment.
> And a many-to-many relationship, in ER, is just that. No fancy tricks
are
> needed, because ER doesn't model an implementation.

Who said anything about implementation ? He would need to use a ... pencil then ? (if you don't allow him to "use" a relationship)

> If you are implementing in a "navigational" (hierarchical or network)
> environment, you use pointers to express relationships.
>
> If you are implementing in a "data centered" (relational or SQL)
> environment, you use foreign keys to express relationaships.

> If you are implementing in an Object oriented environment, I don't know
> what you use.

The question is what HE would use :-)

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